Despite a wealth of structural and biochemical Information on the TF Initiation complex, we still have an Incomplete understanding of the molecular and cellular mechanisms that control TF's hemostatic and thrombotic activities in vivo. During the previous funding period, our studies were focused on the activation of cell surface TF procoagulant activity (TF decryption) and we identified novel players that are connected by the common thread of regulating the generation of TF* micro particles (MP). Our data show that protein disulfide isomerase (PDl) and integrin pi regulate not only the cell surface procoagulant activity of TF, but also the release of TF* MP, specifically from primary cells that significantiy contribute to TF-dependent thrombus formation in vivo. Furthermore, PAR2 signaling controls the TF load of integrin pi* MP, Indicating an amplification loop to increase the prothrombofic activity of MP. The activation ofthe P2X7 receptor decrypts TF on myeloid cells. Unexpectedly, we found that P2X7 also mediates TF activation and the release of TF* MP from smooth muscle cells. Importantly, P2X7-/- and PAR2-/- mice display abnormal thrombus formation and are protected from vascular thrombosis. Together, these data support the novel concept that TF's prothrombotic activity Is under the control of cell signaling events that feed Into pathways relevant for the generation of TF* MP. The continuation of this project will expand on this new dimension of TF thrombogenicity and pursue new concepts that are highly synergistic with the overall goals of this PPG to understand the complex interactions of vessel wall and blood components In thrombus formation and atherothrombosis. In Aim 1, we will test the overall hypothesis that integrin pi and PAR2 signaling controls TF procoagulant activity through trafficking and internalization. In vivo, we will determine how deregulation of these signaling pathways on vessel wall cells or in the hematopoietic compartment promotes thrombosis. In Aim 2, we will study the role ofthe P2X7 receptor In vessel wall and myeloid cells and will test the overall hypothesis that P2X7 signaling is crucial for vascular thrombosis and atherothrombosis by regulating the decryption of TF and the release of TF* MP. RELEVANCE (See instructions): The proposed experiments will elucidate the function of novel players and regulatory cellular circuits In TF- dependent thrombosis and will begin to explore the potential therapeutic benefit of specifically targeting cell signaling pathways to safely attenuate TF thrombogenicity in cardiovascular diseases.